    // 按钮
    let dropdownBtn = document.getElementById("btn");
    // 下拉
    let dropdownMenu = document.getElementById("dropdown");
    // 旋钮
    let toggleArrow = document.getElementById("arrow");

    let toggleDropdown = function () {
        dropdownMenu.classList.toggle("show");
        toggleArrow.classList.toggle("arrow");
    };

    dropdownBtn.addEventListener("click", function (e) {
        e.stopPropagation();
        toggleDropdown();
    });